下面程序的输出结果是 【15】 。 #include <iostream> using namespace std; class base { protected: int a; public: base(){cout<<"0":} }; class basel: virtual public base { public: base1(){ cout<<"1";} }; class base2 : virtual public base { public: base2(){cout<<"2";} }; class derived : public base1,public base2 { public: derived () {cout<<"3"; } } int main () { derived obj; cout<<end1; return 0; }